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Geological rechnccs Inc Page 4 Groundwater Monitoring Report 10 Project Na 662 2 September 24,2003 1 • MW-3 contained the gasoline oxygenate MTBE at 2300Fig/l The well also contained gasoline oxygenates ETBE and TAME at 6 0 and 16 ug/l, respectively • The detections of ETBE and TAME in wells MW-1 and MW-3 are intermittent and appear to be dependent on elevated MTBE concentrations and associated elevated ' reporting limits • Deep screened well MW-104 contained 3 3 ug/1 MTBE This is the fifth consecutive event in which this well has tested positive for MTBE ' • Figure 4 MTBE vs Groundwater Elevation -- MW-3 illustrates a fairly direct relationship between the concentration of MTBE in groundwater and the elevation of groundwater in well MW-3 A linear trend line has been added to the figure to show a ' general decline in both groundwater elevation and MTBE concentrations over time • Neither BTEX nor TPH-G were present in any of the groundwater samples above the laboratory reporting limits ' • Table 3 includes Oxidation-Reduction Potential (ORP) measurements for the site's wells Two of the wells had positive values and two had slightly negative values This ' suggests that there is a limited amount of biodegradation of the contaminant plume occurring This is to be expected, since the primary contaminant is MTBE, which is resistant to biodegradation But the wells with negative values, MW-2 and MW-104, have the lowest contaminant concentrations and this is an anomalous situation One would expect these wells to have higher (ORP) values since they are up gradient and below the contaminant plume, respectively GTI makes the following conclusions • The lateral extent of the groundwater contamination plume is only defined upgradient to ' the northwest by MW-2 • The vertical extent has not been defined since well MW-104 continues to exhibit low concentrations of MTBE However, it is believed to be near the bottom of the contaminant plume ' GTI makes the following recommendations Perform plume definition and evaluate the mass of contaminants present by installing additional monitoring wells GTI has submitted to the SJC PHS/EHD a "Soil & 1 Groundwater Investigation Work Plan" dated October 8, 2001 The work plan was approved with conditions in the SJC PHS/EHD's October 26, 2001 correspondence The first phase of the work, advancing a continuous core boring to determine site lithology, was completed on May 30, 2002 A monitoring well (MW-104) was placed in this boring with a five foot screened interval starting at 24 feet below the water table Since well MW-104 was installed, SJC/EHD staffing has changed In their November t18, 2002 letter correspondence, SJC/EHD has rescinded previously submitted work plans and have called for phased approach to continue the site investigation The phased approached consists of cone penetrometer testing (CPT), followed by 1